Adeno2-SV40 mutants provided complete helper functions of adenovirus associated viruses (AAV), indicating that the helper function resides on the retained portion of the Adenovirus genome and is not inhibited by the insertion of large fragments of the SV40 genome. Infectious DNA extracted from Adenovirus 2 potentiated AAV. Replication of a rodent parvovirus, KRV, was inhibited by phosphonoacetic acid.